1. Field of the Invention
The present invention relates to a deinterlacing method based on an edge-directional interpolation.
In particular, the present invention relates to a method for converting video signals of an interlaced scanning format into those of a progressive scanning format, that is, a deinterlacing method for video signals.
More particularly, the present invention relates to a deinterlacing method for video signals in which an edge-directional interpolation (EDI) is taken into consideration in a conversion of video signals of an interlaced scanning format into those of a progressive scanning format.
2. Description of the Prior Art
In present television systems, a specific scan format so called an xe2x80x9cinterlaced scan formatxe2x80x9d is adopted. In accordance with an interlaced scanning format for NTSC television systems, odd and even lines of 525 scan lines are outputted to a display in an alternating fashion at intervals of a {fraction (1/60)} second for every picture. On the other hand, odd and even lines of 625 scan lines are outputted to a display in an alternating fashion at intervals of a {fraction (1/60)} second for every picture in accordance with an interlaced scan format for PAL systems.
Here, respective pictures outputted at intervals of a {fraction (1/60)} second are referred to as xe2x80x9cfieldsxe2x80x9d. A complete picture consisting of two fields is referred to as a xe2x80x9cframexe2x80x9d.
A field consisting of odd scan lines is referred to as an xe2x80x9codd fieldxe2x80x9d or a xe2x80x9ctop fieldxe2x80x9d whereas a field consisting of even scan lines is referred to as an xe2x80x9ceven fieldxe2x80x9d or a xe2x80x9cbottom fieldxe2x80x9d.
The interlaced scan format, in which every frame is outputted to a display in a state divided into two fields, provides an advantage in that it can reduce the bandwidth of TV signals by xc2xd, as compared to a non-interlaced progressive scan format in which all scan lines of every frame are outputted in a {fraction (1/60)} second.
If TVs of the present NTSC television system, with uses a bandwidth of 6 MHz by virtue of the above mentioned interlaced scan format adopted thereby, did not adopt the interlaced scan format, they would require a bandwidth of about 12 MHz.
In spite of an advantage in that the bandwidth required for signal processing can be reduced, the interlaced scan format involves a drawback in that when a video having horizontal fine line patterns is displayed on a display, those fine line patterns may be chattered at a frame frequency of 30 Hz. That is, a large-area flickering phenomenon may occur.
Where the video displayed on the display contains an object flickering at 30 Hz, there is a problem in that fine line patterns may be viewed in an overlapped state over the object.
The above mentioned phenomena, which result in a degradation in picture quality, are inevitably involved in the interlaced scan format.
However, the advent of digital TV systems has caused picture quality to be considered as a very important factor.
Advanced Television Systems Committee (ATSC) standard for digital TV signals adopts both the progressive scan format and the interlaced scan format.
For instance, TV standard for a size of 704 pels*480 lines adopts a 60 Hz progressive scan format and a 60 Hz interlaced scan format.
In the case of a digital TV receiver adopting a progressive scan format, video signals of an interlaced scan format should be converted into those of a progressive scan format.
On the other hand, where TV signals are to be displayed on the monitor of a PC via a TV receiver card mounted to the PC, it is necessary to convert TV signals of an interlaced scan format into those of a progressive scan format because the monitor can display only videos of the progressive scan format.
Thus, the conversion of video signals from the interlaced scan format into the progressive scan format is essentially required in various cases.
Mainly, there are two methods for the conversion of video signals from the interlaced scan format into the progressive scan format.
The first method is an inter-field interpolation, and the second method is an intra-field interpolation.
A simple example of the inter-field interpolation is a weave method in which one frame is formed by combining one top field and one bottom field.
In accordance with this method, however, horizontal lines disturbing to the eye are formed at a moving portion of the displayed video even though a good display result is obtained in associated with the still portion of the video. This is because there is a timing difference between the two fields.
A more complex example of the inter-field interpolation is a motion-compensated interpolation.
In accordance with the motion-compensated interpolation, motion information is extracted from a frame in order to conduct a desired line interpolation. Based on the extracted motion information, empty lines of the current field are interpolated by the previous field or the further previous field.
In this case, it is important to allow the motion compensation to be accurately carried out.
Meanwhile, a simple example of the intra-field interpolation is a bob method in which one frame is formed using the scanning lines of one field two times.
In accordance with this method, it is possible to prevent horizontal lines disturbing to the eye from being formed at a moving portion of the displayed video. However, there is a complexity in forming frames. Furthermore, the fine portions of the displayed video may be chattered at 30 Hz.
Furthermore, a degradation in vertical resolution is involved in this method. In particular, a distortion in a stepped shape is generated at edge portions of the displayed video.
A more complex example of the intra-field interpolation is an edge-directional interpolation (EDI).
In accordance with this EDI, only the pixels of the current field are used to interpolate the empty lines of the current field. In particular, the directions of edges are detected in order to carry out the interpolation based on the information detected.
Therefore, it is important to detect edge directions accurately.
The present invention is intended to provide an EDI method exhibiting an EDI performance improved over the above mentioned conventional EDI method.
In accordance with the conventional EDI method, the detection of an edge direction is achieved using 6 pixels neighboring to a pixel on a scan line to be interpolated, as shown in FIG. 2a. 
The procedure of detecting the direction of an edge is carried out as follows.
First, respective variations in the value of a pixel, to be interpolated, in three directions passing that pixel are detected using 6 pixels Pa, Pb, Pc, Pd, Pe, and Pf neighboring to the pixel Px.
The pixel value variation in each direction is defined by an absolute difference between the pixel values of two neighboring pixels in that direction, as expressed by the following Equation 1:
AD(45xc2x0)=|Pcxe2x88x92Pd|
AD(135xc2x0)=|Paxe2x88x92Pf|
AD(90xc2x0)=|Pbxe2x88x92Pe|xe2x80x83xe2x80x83[Equation 1]
Next, neighboring pixels to be used for the interpolation are determined, based on differences among the detected pixel value variations in respective directions, as expressed by the following Equation 2:
[Equation 2]                              Px          =                                    (                              Pa                +                Pf                            )                        2                          ,                  (                                                    "LeftBracketingBar"                                  Pc                  -                  Pd                                "RightBracketingBar"                            ⁢                              ⟨                                  "LeftBracketingBar"                                      Pc                    -                    Pd                                    "RightBracketingBar"                                )                                      ⋂                                          "LeftBracketingBar"                                  Pa                  -                  Pf                                "RightBracketingBar"                            ⁢                              ⟨                                  "LeftBracketingBar"                                      Pb                    -                    Pe                                    "RightBracketingBar"                                )                                                                        (        1        )                                          Px          =                                    (                              Pc                +                Pd                            )                        2                          ,                  (                                                    "LeftBracketingBar"                                  Pc                  -                  Pd                                "RightBracketingBar"                            ⁢                              ⟨                                  "LeftBracketingBar"                                      Pa                    -                    Pf                                    "RightBracketingBar"                                )                                      ⋂                                          "LeftBracketingBar"                                  Pc                  -                  Pd                                "RightBracketingBar"                            ⁢                              ⟨                                  "LeftBracketingBar"                                      Pb                    -                    Pe                                    "RightBracketingBar"                                )                                                                        (        2        )                                          Px          =                                    (                              Pb                +                Pe                            )                        2                          ,                  (                                                    "LeftBracketingBar"                                  Pb                  -                  Pe                                "RightBracketingBar"                            ⁢                              ⟨                                  "LeftBracketingBar"                                      Pc                    -                    Pd                                    "RightBracketingBar"                                )                                      ⋂                                          "LeftBracketingBar"                                  Pb                  -                  Pe                                "RightBracketingBar"                            ⁢                              ⟨                                  "LeftBracketingBar"                                      Pa                    -                    Pf                                    "RightBracketingBar"                                )                                                                        (        3        )            
In Equation 2, xe2x80x9cPxxe2x80x9d represents the pixel interpolated. Equation 2 is based on the fact that neighboring pixels in the edge direction in a video exhibit a high correlation, so that they have similar values.
As apparent from the above description, the conventional EDI method is advantageous in that it is simple. However, the conventional EDI method involves several serious problems as follows:
First, the conventional EDI method involves an increased degradation in the accuracy of the edge detection for a video containing an increased amount of noise signal components.
This is because the influence of noise signal components in a video on the calculation of absolute differences increases in that only two pixels are used for the calculation of the absolute difference in each direction.
Second, it may be impossible to accurately detect the edge information in diagonal directions where only video signals of an interlaced scan format are used. This is because there may be a fundamental inaccuracy in the case of FIG. 2b. 
FIG. 2b illustrates the absolute difference characteristics of a pixel Px, which is an optional point on a video having the form of a line extending in a direction of 135. In FIG. 2b, xe2x80x9cAD(45)xe2x80x9d represents the absolute difference between the pixel values of two pixels Pc and Pd, and xe2x80x9cAD(135)xe2x80x9d represents the absolute difference between the pixel values of two pixels Pa and Pf. In this case, it is impossible to expect accurate edge information because xe2x80x9cAD(45)xe2x80x9d and xe2x80x9cAD(135)xe2x80x9d have similar values, respectively.
Third, the number of detectable edge directions in the conventional EDI method is excessively small.
In other words, it is impossible to accurately interpolate all edges passing the pixel Px, to be interpolated, only using the vertical directions of 90 and the diagonal directions of 45 and 135 passing the pixel Px.
Finally, the conventional EDI method may involve an undesirable degradation in resolution, for example, a bluring phenomenon, because the interpolation according to the conventional EDI method is conducted for every pixel.
Due to the above mentioned drawbacks, it is difficult for the conventional EDI method to obtain a good picture quality in the conversion of video signals of an interlaced scanning format into those of a progressive scanning format.
Therefore, an object of the invention is to provide a deinterlacing method based on an EDI in a conversion of video signals of an interlaced scanning format into those of a progressive scanning format, in which the unit of interpolation is extended from the unit of one pixel to the unit of one pixel group, thereby avoiding a degradation in picture quality from occurring in an edge-directional interpolation.
In order to accurately detect edge information even for a video signal containing noise signal components, a plurality of absolute mismatch values are calculated for each of given edge directions, and averaged in accordance with the present invention. An intermediate frame video is formed from an original interlaced field video in accordance with the present invention. An EDI is applied to the intermediate frame image, thereby ensuring an accurate direction detection even in the case in which the selected edge direction corresponds to a diagonal direction. In order to accurately represent the edge direction passing a pixel, the number of possible edge directions is extended to 33 in accordance with the present invention. The unit of interpolation is extended from the unit of one pixel to the unit of one pixel group in accordance with the present invention, thereby avoiding a degradation in picture quality from occurring in an edge-directional interpolation.